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Do you have things to say about "other" flightsims?

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Do you have things to say about "other" flightsims?

Postby Darktrax » Fri Jan 13, 2017 12:27 pm

FIrstly - a great New Year to all!
I don't think I mean stuff like military aircraft carrier training or something Boeing uses at their factory, (but if you have experienced any of that, then do tell)

After an earlier casual effort, I am just about getting started trying FlightGear more seriously. So..

X-Plane - a paid-for sim which the developers claim is not a game. Using something called "blade element theory", which is "an engineering tool that can be used to predict the flying qualities of fixed- and rotary-wing aircraft with incredible accuracy.” Is that a bit like JSBSim?

YSFlight - I don't know anything about it, other than it does not require much computer power to work OK.

Google Earth Flight Simulator - so far, no way could it see the joystick on my Linux machine. No doubt it needs "drivers". I am not even sure the mouse worked OK with it properly, but for me, however great is the photographically derived scenery, a top wide-angle view, transformed to pretend a tilt for viewer eye position, delivers all the wrong motion cues compared to a proper 3D perspective transform of even sparse airport objects.

Microsoft's Flight Simulator - Where the original Cessna 172 became familiar to us all, and once used by some as a casual MSDOS functional test. It is no longer with us, and may have been developed for professional use by companies like Lockheed Martin. It may not have much relevance to our community now, but one can hardly not mention it!
https://en.wikipedia.org/wiki/Microsoft_Flight_Simulator

Condor This is a paid-for "Competition Soaring Simulator", meaning sailplanes .. gliders.
This one keeps the focus on claimed "high accuracy aerodynamics and weather physics". They leave the scenery to what looks like Google Earth derived, though I am not sure.

This is one I have had the opportunity to try out while sat in a full-size glider fuselage mock-up in a room with 3 projector monitors pointed at the walls of a room. All driven off a regular PC with a couple of graphics cards. The messed perspective when trying to judge whether one has flown far enough to do a base leg and final turn was alarming, and just plain unrealistic! That said, the whole aero-tow experience, including encountering the propeller wash, various thermal lifts, incipient spin when overdoing the rudder while going too slow, all of these seemed good, though I would only be able to compare if I got to try out the real aircraft. I guess perhaps too specialist for those who want full airliner flying with engines. Not for me because it runs on various Microsoft Windows, and my PC is a Linux box.

There are bound to be others..
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Re: Do you have things to say about "other" flightsims?

Postby PINTO » Fri Jan 13, 2017 6:05 pm

Not mentioned flightsims that are really popular are DCS, P3D and FSX.
Actively developing the MiG-21bis (link to repo) (link to thread)

http://opredflag.com is an active flightgear dogfighting community (using a system that isn’t bombable)
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Re: Do you have things to say about "other" flightsims?

Postby curt » Fri Jan 13, 2017 6:35 pm

X-Plane's blade element approach is interesting. They divide their airplane up into smaller pieces, do all the math on the pieces and sum the results. X-Plane is kind of like a crude virtual wind tunnel with enough simplification and approximations to allow it to run in real time. This is totally different than JSBSim where you define the exact behavior the aircraft should have.

If you have a physical model (dimensions) of your aircraft, and you know the mass distribution, and you know all the thruster characteristics, then you can give this to x-plane and it will "predict with incredible accuracy" how the plane will fly. Notice that this is marketing language, not necessarily the full reality. The reality is that the x-plane aircraft never flies exactly like real airplane and to make the x-plane model more accurate you need to start tweaking weird things in weird ways. That said, if you have a new design with zero flight data, x-plane will predict how it flies in real time, and that is very very cool.

In many cases you know how an airplane flies and want the sim to match reality as accurately as possible. This is where JSBSim is very powerful. It allows you to closely match real world performance data across a wide flight envelope.

YAsim is also very interesting because it is different yet again. It is sort of like a "lite" version of the blade element approach combined with a solver that fits lift/drag to some basic flight performance numbers you provide. So you still need the 3d shape and mass distribution of the aircraft (like in x-plane), but with YASim you also provide a cruise speed and an angle of attack for a specified approach speed. Yasim uses all this information to "fit" a flight model to it. I really like yasim for the times I know the aircraft shape and weight and also can lookup (or guess at) some simple flight performance numbers.

So what you have with x-plane, jsbsim, and yasim, are 3 totally unique ways to model flight. The choice of which is best depends on which information you are starting with and what results you want to get out. If you don't know anything about how the airplane performs, then x-plane will give you that answer (with incredible accuracy!) If you do have good flight test data and do know exactly how the aircraft performs, then JSBSim will let you match that data even more accurately. If you have some partial knowledge of how the plane flies, but aren't an aerospace engineering, then YASim can do a fairly nice job and get you flying with a pretty plausible model very quickly.

Underneath all these approaches is a foundation of real physics and basic equations of motion.

And of course I should mention there are tools like aeromatic which can help non-aerospace engineers get their models flying quickly with JSBSim. And for those that want to dive even deeper, there are computational fluid dynamic tools (kind of like a virtual wind tunnel) that can help estimate how an aircraft will fly. These offline tools will likely produce even more accurate results than x-plane because they can run off line, use a finer mesh, and simulation more things more fully.)
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Re: Do you have things to say about "other" flightsims?

Postby Bomber » Fri Jan 13, 2017 6:45 pm

It's incorrect to put jsbsim into a box, being incorrect to say "jsbsim does it this way or that way" because it can be configured to do it in many ways... this was the whole point of the beagle pup experiment.
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Re: Do you have things to say about "other" flightsims?

Postby CaptB » Fri Jan 13, 2017 9:04 pm

It would be interesting to know how the FSX FDE does things, looked for it way back that but found little.
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Re: Do you have things to say about "other" flightsims?

Postby Thorsten » Sat Jan 14, 2017 6:29 am

It's incorrect to put jsbsim into a box, being incorrect to say "jsbsim does it this way or that way" because it can be configured to do it in many ways...


On the abstraction level Curt has been writing, it's perfectly correct. It's a matter of input data - JSBSim always requires you to specify coefficients/coefficient functions. It will never work if you give it a 3d mesh (like X-plane) or gross performance characteristics (like YaSim) as input.

There are many ways of obtaining and specifying the coefficient functions (by wind tunnel experiments, by CFD, by tuning them heuristically to the desired output, by modeling them,...) - some of these resemble X-plane, some YaSim - but getting this information is not what JSBSim does, JSBSim starts where you have specified the data.
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Re: Do you have things to say about "other" flightsims?

Postby Richard » Sat Jan 14, 2017 7:25 am

CaptB wrote in Fri Jan 13, 2017 9:04 pm:It would be interesting to know how the FSX FDE does things, looked for it way back that but found little.


FSX (and P3D/ESP) uses a coefficient build up within a predefined model; https://msdn.microsoft.com/en-us/library/cc526961.aspx

an example is here: https://msdn.microsoft.com/en-us/library/cc707065.aspx
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Re: Do you have things to say about "other" flightsims?

Postby CaptB » Sat Jan 14, 2017 9:28 am

@Richard

Indeed, this is the only thing that I found, but there is little on what it actually does with the data internally, only speculation on forums. It seems FS aircraft designers have to resort to some tricks to have somewhat plausible propeller effects on the aircraft and stall behaviour for instance.
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Re: Do you have things to say about "other" flightsims?

Postby Darktrax » Sun Jan 15, 2017 4:33 pm

curt wrote in Fri Jan 13, 2017 6:35 pm:So what you have with x-plane, jsbsim, and yasim, are 3 totally unique ways to model flight.
At my level of FlightGear exploration - so useful! Many thanks!
I have the JSBSim Manual, andI really do want to get to the point I can modify an FDM.
CaptB wrote in Sat Jan 14, 2017 9:28 am:@Richard
It seems FS aircraft designers have to resort to some tricks to have somewhat plausible propeller effects on the aircraft and stall behaviour for instance.

I think this is an efficient approach to augment/modify aircraft behaviour that does not quite match (say JSBsim), or other FDMs. Analagous to the way satellite orbits are predicted using short term tracked Two-line Elements (TLE(s)), where real-time computing of trajectories from Newtonian gravitational physics would be cumbersome, with a high computing overhead.

Even without engine power. modeling stall and spin is *very* difficult! One wing stalls first while the other tips you over while a complicated variable rotational moment from secondary effects adds to the drama.
I think all aircraft can, in the end, spin. Only the drama of getting there varies!

For sailplane riders (me-when I get lucky), the base leg and final turn when too low to risk a spin is fraught with danger.
Having an FDM that models this situation well enough to repeatedly rehearse is something I do wish for.

Condor has lots aimed at my kind of flying, but even with all the goodies, for me, it fails on important aspects of visual perspective.
From what Kurt was saying, X-Plane looks interesting.
As Pinto mentioned, DCS, P3D, FSX. Maybe we can have a first impression?
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Re: Do you have things to say about "other" flightsims?

Postby StuartC » Sun Jan 15, 2017 4:49 pm

Unless your willing to invest serious cash on extras, FSX is pretty basic and dull. Its a Game pretending to be a sim.
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Re: Do you have things to say about "other" flightsims?

Postby stuart » Sun Jan 15, 2017 7:26 pm

Responding to the original post: I had the pleasure of flying a Panavia Tornado procedure trainer a number of years ago. A couple of things were very interesting:

1) The hardware was straight from the aircraft - to the extent that the canopy was closed and locked down before "flight". I still remember reaching forward to the switch on the glare shield to switch the HUD from barometric altimeter to radar, and shifting the throttle lever to the right and the forwards to enable reverse thrust on landing. Very, very cool, and made me realise the importance of simulating the cockpit and control response accurately. Something we can't easily do in a completely computer-based simulator.

2) the visuals were quite limited. The view was fixed with about 120 degrees by 30 degrees view. The graphics quality and resolution were far below what we have now and the sea in particular had bad tiling effects.

3) the trainer must have been 20 years old when I used it (~8 years ago) so there was an entire room full of computers to run it.

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Re: Do you have things to say about "other" flightsims?

Postby C-EYTT » Sat Apr 01, 2017 12:44 am

Rigs of Rods - not strictly a flight simulator, but apparently can do it in a way /vaguely/ similar to X-Plane.
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Re: Do you have things to say about "other" flightsims?

Postby Johan G » Sat Apr 01, 2017 7:07 pm

For some historical flight sims this topic may also be of interest: my first flight sim ;)
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